1. Field of the Invention
The present invention generally relates to a nuclear medical diagnostic device (an emission computed tomography (ECT) device), which applies an radioactive agent to a test subject, and simultaneously measures a γ-ray or a pair of γ-rays emitted by single photon radioactive isotopes (RIs) or positron RIs accumulated in a target portion of the test subject, so as to obtain a tomogram of the target portion.
2. Description of Related Art
For a nuclear medical diagnostic device, that is, an ECT device, the single photon emission computed tomography (SPECT) device and positron emission tomography (PET) device are well known examples thereof.
The SPECT device applies a radioactive agent including the single photon RIs to test subject, and detects the γ-ray emitted from a nuclide by using γ-ray detectors. The energy of the γ-ray emitted from the single photon RIs that are usually used during the inspection of the SPECT device is hundreds of keV. When the SPECT device is used, a single γ-ray is emitted; hence, an incident angle on the γ-ray detector cannot be obtained. Therefore, a collimator is used to detect only the γ-ray incident at a specific angle, so as to obtain the angle information. The detecting method of the SPECT device is as follows. A radioactive agent is applied to a test subject, and the γ-ray generated from the radioactive agent is detected, so as to specify a portion of the test subject where the radioactive agent is consumed relatively more (for example, the portion where cancer cells exist). The radioactive agent contains a material that tends to accumulate on specific tumors or molecules and the single photon RIs, such as Tc-99m, Ga-67, and Tl-201. The obtained data is converted to the data of each voxel through a filtered back projection method and the like. A half life of Tc-99m, Ga-67, and Tl-201 used in the SPECT device is six hours to three days longer than the half life of the RIs used in the PET device.
In another aspect, the PET device applies a radioactive agent including positron RIs to the test subject, and detects an annihilation γ-ray generated by the positrons emitted from the nuclide by using the γ-ray detectors. Theoretically, the positrons may be combined with the electrons of adjacent cells and are annihilated, so the energy of the annihilation γ-ray generated by the positrons emitted from the positron RI used during the inspection of the PET device is fixed to be 511 keV. The annihilation γ-ray generated by the positrons may emit a pair of γ-rays. The detecting method of the PET device is as follows. The radioactive agent and a positron RI O-15, N-13, C-11, or F-18 are applied to the test subject, and the γ-rays generated from the radioactive agent are detected, so as to specify the portion of the test subject where the radioactive agent is consumed relatively more (for example, the portion where cancer cells exist). The radioactive agent includes the material that tends to accumulate on specific cells in the test subject. Fluorodeoxyglucose (2-[F-18]fluoro-2-deoxy-D-glucose, FDG) is an example of the radioactive agent. Through glycometabolism, FDG may be highly accumulated in the tumor tissue, so as to specify the tumor portion. The positrons emitted by the positron emitting nuclide contained in the radioactive agent and accumulated in the specific portion are combined with the electrons of adjacent cells, and are annihilated. A pair of γ-rays having the energy of 511 keV is emitted. The γ-rays are emitted to totally opposite directions from each other (180°±0.6°). If the pair of γ-rays is detected by the γ-ray detectors, it can be recognized that the positrons are emitted between which two γ-ray detectors. By detecting most of the pairs of γ-rays, the portion where the radioactive agent is consumed relatively more may be obtained. For example, as described above, the FDG may be accumulated in the cancer cells with the violent glycometabolism, such that cancer lesions may be found by the PET device. In addition, the obtained data is converted to a radioactive ray generation density of each voxel through the filtered back projection method, so as to pattern the generation position of the γ-ray (the position where the radioactive ray nuclide is accumulated, that is, the position of the cancer cells). O-15, N-13, C-11, and F-18 used in the PET device are RIs with the short half life from 2 min to 110 min.
During the inspection of the PET device, the γ-ray generated when the positrons are annihilated is attenuated in the test subject, so absorption correction data used for the absorption correction must be obtained and the absorption correction data is used to perform the correction. The absorption correction data is as follows. For example, Cs-137 is used as an external ray source, the γ-rays from the external ray source are irradiated on the test subject and the transmission intensity is measured, so as to obtain the data of the attenuation ratio of the γ-ray in the test subject through calculation. The attenuation ratio of the γ-ray in the test subject is estimated by using the obtained absorption correction data, and the data obtained from the emission of the FDG is corrected to obtain a more accurate PET image.
However, the existing nuclear medical diagnostic device has the following problems. That is, in order to improve the diagnostic accuracy, the agent using the nuclide emitting the single photons, an agent using the nuclide emitting the positrons, and other different agents must be simultaneously applied to the test subject. However, the agents cannot be detected and shot simultaneously under the situation. Further, the SPECT device and the PET device are independent from each other, so an expensive device for docking the SPECT device and the PET device docking is required.